In Vietnamese folklore, the phrase “thuận mùa sinh” is used to describe individuals born at an opportune time, in harmony with nature, resulting in good health and intellectual development. Interestingly, this belief is not just a folk tale, as modern scientific studies have also found a correlation between month of birth and cognitive development in children. Notably, those born in September and October tend to exhibit superior physical and intellectual advantages during their early years.
What does science say about children born in September and October?
A study conducted by Harvard University in the United States tracked over 10,000 children for seven years. The findings revealed that children born in September and October had higher average IQ scores compared to their peers born in other months. Additionally, this group of children also exhibited higher average birth weights, indicating a favorable start to their physical development.
Furthermore, statistics also show that many renowned athletes, particularly American football players, were born in these two months. This has led researchers to question whether one’s month of birth could influence their overall development and future success.

Statistics from China reinforce this belief
This phenomenon is not unique to the United States. A similar study conducted at Fudan University in China yielded comparable results. It was found that the highest proportion of first-year university students were born in October. Zhejiang University and Xiamen University also observed a significantly higher number of first-year students born in October. These statistics once again suggest that being born in September or October may provide a favorable start for cognitive and academic development.
Why are September and October considered “thuận mùa sinh”?
To understand this, we need to look at the conception period for these children, which falls in the spring. Spring is a season of rebirth and growth, with mild temperatures and a harmonious natural environment. During the early stages of pregnancy, spring often provides a peaceful mindset for mothers, free from the extreme temperatures and environmental pressures of summer and winter. This plays a crucial role in ensuring stable development during the first trimester, which is crucial for brain and body formation.
Beneficial environmental conditions for both mother and child: Another advantage is that the final trimester falls in autumn, a season of mild temperatures, neither too hot like summer nor too cold like winter. This provides a more comfortable pregnancy experience for expectant mothers, reducing potential health risks during labor.

When children are born in September or October, they enter the spring season approximately three months later, which coincides with important developmental milestones such as rolling over, crawling, and walking. The mild spring weather allows for more freedom of movement, unhindered by bulky winter clothing. Additionally, they are not restricted by the scorching summer heat, encouraging outdoor exploration and physical activity.
This unrestricted movement and exploration during the spring season stimulate cognitive development, contributing to the child’s overall agility and intelligence.
Important note for parents:
While research and statistics suggest that children born in September and October have certain advantages, it is important to remember that the month of birth is not the sole determinant of a child’s intelligence or destiny. Numerous other factors influence a person’s intelligence and success, including genetic factors, nutrition, environment, education, and familial love and support.
Therefore, if you are planning to have a child, there is no need to solely focus on giving birth in September or October. Instead, it is more important to prioritize financial stability, good health, a positive mindset, and knowledge about child-rearing.
While it is acknowledged that children born in September and October tend to have advantages in terms of cognitive and physical development, as supported by both modern science and traditional wisdom, each child is unique and possesses their own distinct potential. Parents can enhance their children’s intelligence by providing a nurturing and stimulating educational environment.